Method for electroless copper plating



United States Patent 3,259,559 METHUD FOR ELECTROLESS COPPER PLATINGFrederick W. Schneble, In, Oyster Bay, John F. McCormaclr, RoslynHeights, Rudolph J. Zeblislry, Hauppauge, John Duff Williamson, MillerPlace, and Joseph Polichette, South Farmingdale, N.Y., assignors, bymesne assignments, to Day Company, N.V., a Curacao corporation FiledAug. 22, 1962, Ser. No. 218,656 The portion of the term of the patentsubsequent to June 25, 1980, has been disclaimed 45 Claims. (Cl. 204-38)The present invention is a continuation-in-part of copendingapplications Ser. No. 785,703, filed January 8, 1959, and now abandoned;Ser. No. 33,361, filed May 31, 1960, now Patent No. 3,146,125; and Ser.No. 26,401, filed May 3, 1960, and now Patent No. 3,095,309.

This invention relates to novel and improved methods for metallizinginsulating supports and to the products which result from such methods.

More particularly, the present invention relates to imposing by chemicalmeans strongly adherent and rugged deposits of metal on insulatingsupports and to the products which result from such methods.

Although applicable whenever it is desired to strongly adhere a metalcoating to an insulating base, as for example, for decorative effect, orto make electrical conductors of a wide variety of shapes andconfigurations, the procedures for metallization disclosed herein areparticularly useful for making printed circuits from cheap, lowgrade,readily available electrical insulating base materials or 1basematerials coated with electrical insulation mater1a s.

It is a primary object of the present invention to provide improvedchemical methods for imposing a uniform, rugged, firmly adherent,non-porous, bright and ductile deposit of copper on an insulatingsurface.

Another object of the invention is to provide chemical methods forimposing such a deposit of copper on irregularly shaped, complex, orcurved insulating surfaces.

Still another object of this invention is to provide improved chemicalmethods for imposing a rugged and adherent conductor pattern on cheap,readily available insulating base materials.

A further object of this invention is to provide improved printedcircuits which are rugged and durable, and which can Withstand roughmechanical handling and heat shock.

Another object of this invention is to provide methods for makingimproved printed circuits in which the support for the circuits hasimproved insulating properties.

An additional object of this invention is to transform cheap, insulatingbase materials into commercially attractive electrical conductivecomponents by chemical means.

Other objects and advantages of the invention will be set forth in partherein and in part will be obvious herefrom or may be learned bypractice with the invention, the same being realized and attained bymeans of the steps, instrumentalities and combinations pointed out inthe appended claims.

The invention consists in the novel parts, constructions, arrangements,combinations and improvements herein shown and described.

The accompanying drawings referred to herein and constituting a parthereof, illustrate embodiments of the invention and together with thedescription serve to explain the principles of the invention.

Although the invention will be described with particular reference toprinted circuits, and although fabrication of printed circuitsconstitutes a primary and preferred application, it should be understoodthat the invention is 3,259,559 Patented July 5, 19,66

ice

not limited to printed circuits but is applicable to metallizinginsulating surfaces broadly.

Heretofore, it has been suggested to manufacture printed circuits byprinting on an insulating backing a design of the circuit by means ofvarious inks containing receptive particles and then electrolesslydepositing a conductive material on the receptive particles.

Two main problems have been encountered in such a procedure. The firstproblem concerns the adhesion between the receptive particles and thebase. Techniques previously described include seeding a base materialwith aqueous acidic solutions of precious'metal ions such as palladiumchloride .For example, the insulating material may be immersed in a bathcomprising an aqueous acidic solution of stannous chloride and palladiumchloride to render selected areas of the insulating material sensitiveto the reception of an electroless metal deposit. Such sensitizationbaths, however, have many disadvantages. First and foremost, theadhesion between the precious metal deposit and the subsequentlyelectrolessly deposited metal has been found to be tenuous. As a result,when the resulting circuits are subjected to rugged mechanical handling,or heat shock, such as by dip soldering, there is a tendency for theconductive layer to crack or pop free of the base, thereby disruptingthe circuit. Additionally, such treating solutions are ponderous andexpensive to employ, and must be carefully regulated if good results areto be achieved.

The second problem encountered in metallizing insulating bases by thetechnique under discussion resides in the electroless metal bath.Heretofore, a wide variety of electroless metal plating bath processeshave been proposed for the deposition of thin layers of metal uponinsulating surfaces, ceramics, plastics, and other materials. Ingeneral, none of these have been useful to any substantial degree forthe electroless deposition of copper on metal surfaces. The prior artbaths have produced copper deposits which are brittle, break undervibration and bending, and otherwise exhibit poor ductility, althoughmany of the baths are commercially useful within recognized limits.Additionally, the deposits produced by most prior electroless copperdepositing baths do not produce copper deposits which are bright.Rather, the deposits from conventional baths ordinarily exhibit a dullsurface of poor color. Frequently, the prior art baths yield a muddylayer of copper. Additionally, the baths of the prior art processes areoften subject to instability, and impurities rapidly accumulate in thebaths, the bath finally reaching a condition such that it spontaneouslydecomposes, throwing out copper as a useless precipitate.

These and other disadvantages of the prior art are overcome by thepresent invention.

According to this invention, a process for metallizing insulatingsurfaces has been discovered which comprises providing an insulatingbase material with adhesively bound, finedly divided, solid particles ofan agent catalytic to the reception of electroless deposited metal, andthen subjecting the resulting base material to a new and im provedelectroless copper bath to be disclosed.

When the catalytic compositions and the electroless depositing bathsdescribed herein are employed in the manner and in the sequence to bedescribed, there is produced on the base material a dense, uniform,ductile, bright, conductive copper deposit which is firmly andtenaciously adhered to the base material or substrate.

It is the combination of the catalytic composition to the electrolesscopper depositing baths disclosed herein that leads to the production ofnew and unexpectedly improved coatings of copper on an insulating base.

When the catalytic composition and the electroless copper depositingbaths disclosed are employed in making printed circuits, many advantagesover the conventional commercial procedures are obtained. According tothis process, copper is applied only where desired. No etching isrequired, and no copper is thrown away. The process is readily adaptableto mass production techniques, and miniaturized circuits having firmlyadherent conductive patterns are obtained. Additionally, the copperdeposit forming the conductive pattern is ductile and bright, and itsthickness can be controlled to close limits. The fact that the copperdeposit is ductile is highly significant. Because of its ductility, theconductor pattern is strongly resistant to both mechanical and thermalshock and can readily withstand both rough mechanical handling andsoldering, including dip soldering. Heretofore, so far as applicants areaware, it has not been possible to deposit a ductile copper layer usingelectroless techniqucs. Additionally, the process is economical andrequires a minimum amount of control. Further, the copper deposit can beapplied on practically any base material, regardless of size, shape orconfiguration, and can be subsequently readily coated or reinforced withother metals by electroless dip techniques or other procedures to impartspecial characteristics or properties to the circuits as a whole, orportions thereof.

A limiting factor in the production of printed circuits by theconventional print and etch technique is that the thickness of the foil,ordinarily produced by rolling copper, has a lower limit of about 0.7 to1.3 mils. Frequently, for special purposes, it is desirable to have aconductor pattern which is less than 0.7 mil, i.e., inthe order of about0.1 mil or even lower. With the techniques described herein, uniformlayers of ductile copper having a thickness of iess than 1.3 mils, or inthe order of about 0.1 mil to 7 mils, or even less, may readily beachieved.

The catalytic compositions forming a part of the present inventioncomprise an adhesive resin base having dispersed throughout finelydivided particles of an agent which is receptive to electrolesslydeposited copper.

The receptive agents dispersed throughout the resin base are cheap,readily available, particulate, finely divided metal or metal oxides,such as titanium, aluminum, copper, iron, cobalt, zinc, titanous oxide,copper oxide, and mixtures of the foregoing.

Particularly good results are achieved when the re ceptive agent iscuprous oxide and this material is preferred for use. Cuprous oxide isitself an exceptionally good insulator of electricity. Additionally,when reduced, as by treatment with an acid, the cuprous oxide may bechanged to metallic copper to initially form the conducting portion ofthe desired printed circuit design which may then be further built up byelectroless deposition by immersion or otherwise treating with theelectroless copper depositing baths to be disclosed.

The catalytic compositions of the present invention may take a varietyof forms.

For example, the insulating base members contemplated for use are mostfrequently formed of resinous material. When this is the case, theactive agent disclosed herein, and especially copper oxide, in finelydivided form, may be incorporated into the resin by milling,calendering, or other conventional methods after which the resin is setto form the base.

Alternatively, a thin film or strip of unpolymerized resin havingparticles of the active agent suspended therein might be laminated to aresinous insulated base and cured thereon. In this embodiment, theinsulating base could be a resin impregnated laminate of paper or clothsheets or Fiberglas.

In the preferred embodiment an ink comprising an adhesive resinousmaterial having dispersed therein finely divided particles of thecatalytic agent is printed on the surface of an insulating support andcured thereon.

Regardless of the manner in which it is incorporated in or on the basematerial, the catalytic agent is present in a finely divided form andpreferably passes 200 mesh,

- vinyl acetate, and the like.

US. Standard Sieve Series. Ordinarily from a small fraction of 1% toabout of the active agent is admixed with adhesive resinous material toform the catalytic composition, but this concentration will depend to alarge extent upon the materials used, and upon the time in which thecatalytic compositions are allowed to remain in the electroless platingbath.

The resins into which the particles of the active material are dispersedpreferably comprise, in combination, a thermosetting resin and aflexible adhesive resin. Typical of the thermosetting resins may bementioned oil soluble phenolic type resins, such as fusible copolymersof phenol, resorcinol, a cresol, or a xylenol with an aldehyde or withfurfural. Also may be mentioned the polyester resins, which are wellknown in the art and are prepared by reacting dicarboxylic compoundswith dihydric alcohols, for example, by the reaction of phthalic ormaleic anhydride with mono-, dior polyethylene glycols. The polyesterresins are ordinarily dissolved in styrene monomer and cross-linked byreaction with the styrene. As the thermosetting resin may also bementioned epoxy resins, such as the reaction product of epichlorohydrinwith bisphenol A.

Typical of the flexible adhesive resins are the epoxy resins, polyvinylacetal resins, polyvinyl alcohol, poly- Also as the adhesive resins maybe mentioned chlorinated rubber and butadiene acrylonitrile copolymers.

The adhesive resins of the type described have appended thereto polargroups, such as nitrile, epoxide, acetal, and hydroxyl groups. Suchadhesive resins copolymerize with and plasticize the thermosettingresins, and impart good adhesive characteristics through the action ofthe polar groups.

The thermosetting resin portion of the composition is required in orderto afford resistance to heat upon soldering, and also to protect againstdecomposition when subjected to the electroless copper bath. Athermosetting resin alone, however, will not ordinarily have adequatetackiness or sufiicient flexibility to resist heat shock; and would havenegligent resistance to peeling of long conductor patterns from thesurface. Admixture of adhesive resins such as those disclosed overcomethe deficiencies of the thermosetting resins, and together, thethermosetting and. adhesive resins provide an especially suitablecomposition for carrying the catalytic agents and for adhesively bindingthem to the base.

Particularly suitable for use as the adhesive resin for certainsubstrates is a combination of a phenolic type resin and an epoxy resin.The most common epoxy resins for use in the resinous composition arecopolymers of epichlorohydrin (l-chloro-2,3-epoxy propane) withbisphenol A (2,2-p-hydroxy phenyl propane) which have melting pointswithin the range of 20 F. to 375 F. and molecular weights of about 350to 15,000.

Although epichlorohydrin is the most important organic epoxide employedin the formation of the epoxy resins, other epoxides such as, forexample, 1,2,3,4-diepoxy butane may be used. Similarly, epoxy resinsderived from phenols other than bisphenol A are suitable for use. Suchresins include, for example, the reaction product of epichlorohydrinwith resorcinol, with phenols derived from cashew nut oils, withhydroquinone, with 1,5-dihydroxy naphthalene or with 2,2,5,5-tetrabis-(4-hydroxy phenyl) hexane. Phenolic intermediates of the resol type,hydrazines and sulfonamides, such as, for example, 2,4-toluenedisulfonamide, may also be used for reaction with an organic epoxide toproduce epoxy resins suitable for use. Aliphatic epoxy resins are alsosuitable. Such resins are, for example, the reaction product ofepichlorohydrin with glycerol, with ethylene glycol or withpentaerythritol.

The phenolic type resin may be a copolymer of a. phenol, resorcinol, acresol or a xylenol with an aldehyde or with furfural. Thus, it may be acopolymer of phenol or a substituted phenol with formaldehyde or aformaldehyde-yielding material, such as, paratormaldehyde orhexamethylene tetra-amine. The phenolic resin is preferably of the oilsoluble type. As examples of thermosetting phenolic type resins whichmaybe used may be mentioned copolymers of formaldehyde with p-cresol,p-ethyl phenol, p-tert butyl phenol, p-tert amyl phenol, p-tert octylphenol, p-phenyl phenol, di-isobutyl phenol, or a bisphenol, such as4,4-isopropylidene diphenol or 2,2-bis(p-hydroxy phenyl) propane. It maybe of the modified type, such as, for example, one which has beenmodified with copal or rosin to cause it to be oil soluble.

The phenolic type resins are, themselves, curing agents for the epoxyresins, and even those which are, themselves, permanently fusible form atough, adherent film in combination with an epoxy resin which isprobably the result of a cross-linking between the epoxy resin and thephenolic type resin. However, the resinous compositions may contain anadditional curing agent. This curing agent may be another resin, suchas, for example, a polyamide resin or a melamine-formaldehyde resin, orit may be, for example, a dibasic acid, such as, for example, phthalicanhydride, an amine, such as, for example triethanolamine, diethylenetriamine or metaphenylene diamine, or an amide, such as, for example,dicyandiamide.

When using a thermosetting type of phenolic resin, 3. curing agent forthe phenolic, such as, for example, one of the amines mentionedhereinabove as a curing agent for epoxy resin maybe employed.

The active agent, it should be clear, is incorporated into the resinouscompositions in such a way that the agent is dispersed throughout theresin, and present in the resin, upon solidification, at numerousindividual sites. Because of this dispersion, the particles of thereceptive agents are not in contact with one another and accordingly,the catalytic compositions disclosed herein are nonconducting. Ofcourse, when the active agent is itself non-conducting, such as cuprousoxide, or .titanous oxide, this factor is not important. When metalssuch as copper, iron, and so forth, are employed as the active agent,however, the dispersion of the active particles throughout the resinbecomes important. Were conducting particles to be incorporated into thecatalytic compositions in such a manner that they were in intimatecontact with one another, it would be impossible to prepare printedcircuits from such compositions using the so-called reverse method. Inthis method, the catalytic composition would be adhered to the over-allsurface of the base material or the base material would itselfconstitute the catalytic composition, and selected portions thereofwould then be masked, leaving exposed the conductor pattern. The basewould then be immersed in the electroless copper bath to deposit copperon the exposed areas. Were the catalytic composition employedconductive, leakage would occur between the lines of the conductorpattern through the catalytic composition. Obviously, such a situationcould not be tolerated.

When large amounts of the active agent are employed, as compared to theresin, relatively small amounts of resin bind the uppermost or surfaceparticles of the active agent. Accordingly, electroless copper canreadily deposit on the active agent on the surface. When small amountsof the active agent are employed in comparison to the resin, e.g., 0.25to by weight, it may be that the active agent at the surface of thecatalytic composition will be completely coated by the resinousmaterial. In this situation, it may be necessary to abrade the surfaceso that the particles will be exposed to the electroless plating bath.If, in this situation no abrasion is used, it will be necessary toexpose the surface to the electroless plating bath for several hoursbefore the initial copper deposit will form.

When copper oxide is used, it is preferable to activate the cuprousoxide by treatment with an acid, to convert at least a portion of thecuprous oxide particles at the surface of the ink to copper. Preferredfor use is sulfuric acid. Other reducing agents which are acceptableinclude aqueous solutions of phosphoric acid, acetic acid, sulfuricacid, hydrofluoric acid, dithionates, hypophosphites, and the like.Nitric acid may also be used but it is not quite as desirable as theothers since :it dissolves the copper formed at a rather high rate.Alkaline formaldehyde solutions including the electroless copper bathsdisclosed herein will also reduce the cuprous oxide.

Among the wide variety of adhesives which may be used when it is desiredto prepare the catalytic compositions in the form of inks are thosecompositions disclosed in US. Patent Nos. 2,532,374 and 2,758,953. Inthis embodiment, the receptive agent, as will be clear, is imparted intothe adhesive base in such a way that the receptive agent is dispersedthroughout the base medium, and present in the base medium at numerousindividual sites. Typical examples of catalytic inks suitable for use inprinting conductor patterns on an insulating base are given below:

EXAMPLE 1 G. Xylene 50 Diacetone alcohol 75 Parlon l0 cps. 50Phenol-formaldehyde (oil soluble) l0 Butadiene-acrylonitrile rubber 2OCab-O-Sil 3 Cuprous oxide 70 EXAMPLE 2 Butadiene acrylonitrile rubber15.5 Diacetone alcohol 72 Nitromethane 72 Phenol-formaldehyde resin (oilsoluble) 7.5 Cab-O-Sil t 4 Ethanol 3 Parlon l0 ops. 10 Xylene 50 Cuprousoxide EXAMPLE 3 Butadiene acrylonitrile rubber 15.5 Diacetone alcohol 50Nitromethane 50 Phenol-formaldehyde resin (oil soluble) 7.5 Parlon 10cps. 3 Toluene 2O Cab-O-Sil 3 Ethanol 3 Cuprous oxide 60 EXAMPLE 4Butadiene acrylonitrile rubber 15.5 Diacetone alcohol .Q 50

Nitromerthane 50 Phenol-formaldehyde resin (oil soluble) 7.5 Cab-O-Sil a3 Ethanol 3 Cuprous oxide 60 EXAMPLE 5 Toluene 50 Diacetone alcohol 50Butadiene acrylonitrile rubber 10.5 Phenol-formaldehyde resin(oil-soluble) 7.5 Parlon l0 cps. 5 Ethanol 5 Cab-O-Sil 6 Cuprous oxide50 7 EXAMPLE 6 Epoxy resin Butadiene acrylonitrile rubber 15 Diacetonealcohol 50 Toluene 50 Phenol-formaldehyde resin (oil soluble) 11 Cuprousoxide 60 In the above examples, Parlon is a. chlorinated rubber fromHercules Powder Company. The epoxy resin of Example 6 is DER 332, soldby Dow Chemical Company, and is the reaction product of epichlorohydrinand bisphenol A. It has an epoxy equivalent of 173 to 179, an averagemolecular weight of 340 to 350 and a viscosity at C. of 3600 to 6400.Cab-O-Sil is a tradename for silica aerogel.

To prepare the coating compositions or inks disclosed in Examples 1 to6, the resins are dissolved in the solvents and milled with the pigmentson a three roll mill.

The viscosity of compositions having the formulae of Examples 1 to 6will ordinarily vary between about 5 and 100 poises at 20 C.

The catalytic inks may be applied to the panel in any convenient manner.For example, when a direct process for making printed circuits isemployed, the circuit pattern of the ink may be imposed on theinsulating base by screen printing or offset printing techniques. Whenthe reverse process is employed, the insulating base may be coated withthe catalytic ink, as by dipping, spraying, calendering, and the like,and then portions thereof masked .to leave exposed the conductorpattern. When the catalytic inks are used to produce plated throughholes, the ink may be drawn into the holes by vacuum. Alternatively, thepierced panels may be dipped into the inks, and then vibrated to removeexcess ink from the holes.

After treatment of the panel with the catalytic ink, the adhesive baseof the ink may be partially or fully cured by heating, thereby firmlybonding the adhesive ink with its contained receptive agent to theinsulating base memher.

The insulating base materials used to make the printed circuits must beable to withstand the temperatures which will be encountered inprocessing and in use. Preferable for use as insulating base materialsare sheets of ceramic, phenol-formaldehyde, melamine-urea, vinylacetatechloride copolymer, rubber, epoxy resin polymers, epoxyimpregnated Fiberglas, and the like.

After curing, the catalytic ink may be lightly abraded by rubbing itssurface with steel wool, sand paper or other abrasive material so thatthe receptive particla which make up the active sites are exposed. Asindicated hereinabove, this step is not always necessary and depends toa large extent upon the exact nature of the adhesive compositionemployed in the ink and upon the concentration of the receptiveparticles in the ink.

Electroless plating baths preferred for use in the present inventionconsist essentially of a soluble copper salt (e.g., copper sulfate,cupric chloride, cupric nitrate, copper gluconate, cupric acetate, andthe like); a complexing agent for the cupric ions (e.g., Rochelle salts;ethylene diamine tetraacetic acid and its sodium salt; nitrolotriaceticacid and salts thereof; N-hydroxyethylethylenediarnine triacetate;triethanolamine; sugar, including sucrose, dextrose, lactose, levuloseor maltose; mannitol; sorbitol gluconic acid and the like; an alkali oralkaline earth metal hydroxide, such as sodium or potassium hydroxide;an active reducing agent such as formaldehyde; and a small amount of acomplexing agent for cuprous ion, such as cyanide salts, e.g., sodiumand potassium cyanide, acrylonitrile, lactonitrile, glyconitrile,thiourea, allyl alcohol, and ethylene. Preferred for use as thecomplexing agent for cuprous ion are the cyanide salts, such as sodiumand potassium cyanide, acrylonitrile, lactonitrile, and glyconitrile.

The quantities of the various ingredients in the bath are subject towide variation, within certain ranges which may be defined as follows:

Copper salt from 0.5 g. to saturated solution (0.002 to .15 mol. ormore).

Alkali metal hydroxide to give pH 10.5 to 14.

Formaldehyde 0.06 to 3.4 mol.

Complexing agent for cupric ion 0.5 to 2.5 times moles of copper.

Complexing agent for cuprous ion (0.00002 mol. to 0.06

mol.).

Watersufficient to make 1 liter.

The ratio of the copper salt to the complexing agent for cupric ionshould be such that there are from 0.5 to 2.5 as many moles of cupriccomplexing agent as of copper, e.g., 5 grams of CuSO -5H O requires from2.5 to 8.5 grams of Rochelle salts.

Sodium hydroxide and sodium cyanide are preferred over the correspondingmore costly potassium and other alkali metal salts, which are of greatermolecular weight.

Rochelle salts, the sodium salts (mono-, di-, tri, and tetrasodiumsalts) of ethylenediaminetetraacetic acid, nitriltriacetic acid and itsalkali salts, gluconic acid, gluconates, and triethanolamine arepreferred as cupric ion complexing agents, but commercially availableglucono -5 lactone and modified-ethylenediamineacctates are also useful,and in certain instances give even better results than the pure sodiumethylenediaminctetraacetates. One such material isN-hydroxyethylethylenediaminetriacetate.

Cupric sulfate is preferred as the copper salt, but other soluble coppersalts may be used, such as the nitrate, chloride and acetate.

In considering the general formulae for the electroless copper baths andthe specific working formulae which are set forth below, it should beunderstood, that as the baths are used up in plating, the cupric salt,and the formaldehyde reducing agent may be replenished from time totime, and also that it may be advisable to monitor the pH and cuprousion complexing agent content of the bath, and to adjust these to theiroptimum value as the bath is used.

The baths are ordinarily used at slightly elevated temperatures, such asfrom 35 to C. although many of them may be used at even highertemperatures. As the temperature is increased, it is usual to find thatthe rate of plating is increased, and that the ductility of the depositis increased to a slight extent, but the temperature is not highlycritical, and within the usual operating range, excellent deposits areproduced which exhibit greatly improved properties over those obtainedwith conventional baths.

With electroless copper plating baths used herein, the efiiciency ofcopper recovered by electroless deposition from the bath often exceedswhich is much greater than has heretofore been observed in working withcon ventional baths.

The cuprous ion complexing agent in the bath is an important feature andserves to prevent or minimize the formation of cuprous oxide in thebath, and also appears to inhibit the formation of resulting hydrogen inthe electroless deposited metal. Without the cuprous ion complexingagent, e.g., cyanide and the like, the bath has been found to beunsatisfactory as a stable plating solution, and the electroless copperdeposit has been found to be smudgy and of a poor appearance on thesurface opposite the adhering base. Additionally, it has been discoveredthat without the cuprous ion complexing agent, a ductile deposit ofelectroless copper is not obtained.

The baths to be described herein will ordinarily deposit a coating ofelectroless copper of a thickness of about 1 mil, within between about10 and hours, depending on the composition, pH, temperature, and related factors.

9 Examples of the electroless copper depositing baths suitable for usewill now be described.

Water, remainder.

This bath is preferably operated at a temperature of about 55 C., andwill deposit a coating of ductile electroless copper about 1 mil thickin about 51 hours.

Water, remainder.

This bath is preferably operated at a temperature of about 56 C., andwill deposit a coating of ductile electroless copper about 1 mil thickin about 21 hours.

EXAMPLE 9 Moles/1. Copper sulfate 0.02 NaOH 0.125 NaCN 0. 0002 HCHO 0.47Rochelle salt 0.0425 Water, remainder.

EXAMPLE l Moles/l. Copper sulfate 0.04 NaOH 0.19 NaCN 0.0002 Rochellesalt 0.0425 HCHO 0.47 Water, remainder.

EXAMPLE 11 Moles/l. Copper sulfate 0.04 NaOH 0.19 NaCN 0.0006

HCHO 0.47 Rochelle salt 0.0425 Water, remainder.

EXAMPLE 12 Moles/l. Copper sulfate 0.04 Sodium hydroxide 0.19 NaCN0.0002

HCHO 0.47 Rochelle salt 0.064 Water, remainder.

EXAMPLE 13 Moles/1. Copper sulfate 0.02 NaOH 0.125 NaCN 0.0002 HCHO 0.40Sodium citrate 0.051

Water, remainder.

10 EXAMPLE 14 Moles/l. Copper sulfate 0.02 NaOH 0.05 NaCN 0.0002 HCHO0.1- Trisodium N-hydroxy ethylenediaminetriacetate 0.024

Water, remainder.

The following examples are illustrative of the improved methods ofmaking printed circuits according to the teachings contained herein.

' EXAMPLE 15 An insulating base is formed by uniformly mixing grams ofCiba 6005 which is the reaction product of bisphenol A andepichlorohydrin which has a viscosity of 4500 centipoises and an epoxyequivalent of and adding to it an equal weight of cuprous oxide whichpasses 200 mesh .and milling with the pulverulcnt copper oxide particlesfor 1 to 2 minutes, which makes for a mixture which is relativelyuniform. This uniform mixture is ready for immediate use or may be setaside for later use. It has an amine hardener, in this case 70 grams ofdiethylene triamine blended with it by constant turning, cutting andrubbing for about 2 minutes. It is then transferred to a mold by meansof which it is given the shape desired. Heat may be applied to speedsetting of the epoxy resin loaded with cuprous oxide particles so thatthe reaction is complete in a period of about one hour.

One surface of the insulating base thus formed is provided with aresist, portions of which have been removed, said portions masking outthe circuit design which it is desired to form. An aqueous solution of30 Baum sulfuric acid is then applied to the resist covered surface. Thestrength of the acid is not particularly critical and acid strengths offrom 5 to 40 Baum have proven quite acceptable. The acid is allowed toremain in contact with the resist covered surface for 10 minutes.-Contact of from 5 to 15 minutes is the usual period of time in which thecuprous oxide particles which are unprotected by the resist are reactedupon by the acid and converted to metallic copper. The acid is thenremoved by a thorough rinsing and the insulating base is then immersedin the electroless copper bath of Example 7 for about 51 hours. Auniform, adherent, bright, ductile copper deposit about 0.001 inch thickwas built up during this period of time. The deposit was tenaciouslyadhered to the base and could only be removed by scraping. The depositcould be readily soldered, both by dipping in a hot solder bath, and byhand soldering.

support to a depth of about of an inch and cured thereon. This depth maybe varied on either side of that used here but A of an inch is the mostuseful for any practical purpose. After curing this lamina therebybonding it to the insulating base substance, the other steps of theprocess, i.e., masking, developing with acid and electrolessly plating,are carried out as in Example 15, and comparable results are obtained.

EXAMPLE 17 Example 15 was repeated with the exception that the molded,cuprous oxide loaded insulating base, following formation, is pierced todefine apertures, holes or crossover points between the top and bottomsunfaces of the base. The apertures could be formed by drilling orcutting. When treated in the acid and then immersed in the electrolesscopper depositing bath, electroless copper deposits on the lateral sidessurrounding the holes as well as on the circuit design. As will readilybe appreciated, this technique aifords an extremely simple and facilemethod of making printed circuits with plated through holes.

The cuprous oxide loaded base of Example 15 also permits formation ofprinted circuits in a solid block of insulating material, as will beclear from the following examples.

EXAMPLE 18 A cylindrical block of cuprous oxide loaded resin wasprepared following the procedure of Example 15. The suufaces of thecylindrical block are then covered completely with a resist. Holes arethen drilled into the cylindrical block to form a pattern ofinterconnecting channels. Drilling .the holes exposes the catalyticagent at myriad individual sites on the walls defining the holes. Thecylindrical block is then treated with acid and immersed in theelectroless copper bath, as described in Example 15. An adherentuni-form, bright, ductile copper deposit is thereby formed on thelateral Walls of the holes to form a printed circuit which is entirelyencased in the cylindrical block.

If desired, of course, a circuit pattern could also be imposed on theexterior surfaces of the block. The conducting pattern on the surfacecould connect or not connect with the circuit in the interior of theblock.

T he importance of such a technique in forming micromini-ature circuitswill readily be apparent to those skilled in the art.

In Examples 17 and 18, the solid block of material used to form theprinted circuit could of course be any geometrical shape, such asspherical, tetragonal, hexagonal and the like.

EXAMPLE 19 Another variation of this invention is the provision ofcuprous oxide in an adhesive resin-based ink which may be printeddirectly on an insulating base support such as epoxy impregnatedFiberglas. A suitable ink tormulation for use in this embodiment is madeup by weight as follows:

Parts Phenol-formaldehyde resin (alcohol soluble) 60 Polyvinyl butyralresin 40 Ethanol 100 Cuprous oxide (powder, pass 200 mesh) 150 Powderedsilica (methyl isobutyl ketone) sufiicient to adjust viscosity to about200 poises.

The resin based ink circuit thus outlined is cured, bonding it to theresin insulating base. The cuprous oxide particles are reduced tometallic copper by means of contacting the cured resin-based inkcontaining cuprous oxide particles with an acid and building up thecircuit in the same manner as in Example 15.

If plated through holes are desired, these may be achieved by piercingthe insulating base support prior to or following printing, and coatingthe lateral walls surrounding the holes with the catalytic ink, andcuring. The panel is then treated with the acid and then with theelectroless copper bath to deposit copper on the conductor pattern andon the lateral walls surrounding the holes.

EXAMPLE 20 An adhesive containing a small amount of copper oxide (Cu O)is prepared as follows:

Parts by wt. Butadiene-acrylonitrile copolyrner 23 Phenol-formaldehyderesin 10 Zirconium silicate 107 Silica (20) 4 Cuprous oxide 0.5Isophorone Xylene 31 1 Medium high acrylonitrile content.

combination of 5 parts oil soluble, heat reactive, solid resin, ALP.144-162 F. and 5 parts alcohol soluble, oil soluble, heat reactive solidresin.

The rubber is dissolved in part of the solvents and the phenolic resindissolved separately in the rest of the solvents. The two solutions,cuprous oxide and the pigments are blended in a three roll paint mill.The circuit design is screen printed with the resulting ink on anepoxy-impregnated Fibe-rglas laminate and cured. The cured print of thecircuit is immersed in 20 Baum sulfuric acid solution for 10 minutes, Itis then removed, washed free of sulfuric acid and immersed in theelectroless plating bath described hereinabove. Again, plated throughholes may be formed, if desired, using the procedure of Example 19.

EXAMPLE 21 A molding composition containing 10% cuprous oxide isprepared as follows:

Parts (1) Epoxy resin (reaction product of bisphenol A andepichlorohydrin having an epoxide equivalent of to 200 and an averagemolecular weight of 350 to (2) Cuprous oxide l0 (3) Polyamide resin(having an amine value of 210 to 230, the condensation product ofdimerized or trimerized fatty acids with aryl or alkyl polyamines) 60(4) Zirconium silicate a- 97 (5) Silica (20) 4 The epoxy resin, cuprousoxide and pigments are blended together in a three roll paint mill, andthe polyamide resin was warmed until readily workable and blended withthe mixture from the mill by constant turning, cutting and rubbing for 5minutes. The mix was cast in a mold and cured at 250 F. for 45 minutes.The fabrication of the printed circuit was carried out as in Example 1.

EXAMPLE 22 Examples 15 to 21 are repeated with comparable results usingfinely divided particles of titanium, aluminum, copper, iron, cobalt,zinc, and titanous oxide as the catalytic agent. With these agents, theacid treatment was not necessary. Best results were achieved when thecatalytic composition was slightly abraded prior to exposure to theelectroless copper bath.

EXAMPLE 23 Holes are drilled in a cylindrical block of acrylic resinhaving a diameter of inch and a height of 1 inch. The holes are drilledat various angles and various directions so that they interconnect eachother at selected positions, as shown, for example, in FIGURE 4.

The holes are cleaned by treating with a mild alkaline cleaner, and thenthe holes are coated with the catalytic ink of Example 1. Residual inkis removed from the surface of the cylinder. The cylinder is thentreated with acid and immersed in the electroless copper depositingbath. An adherent, bright, ductile copper deposit is formed on lateralwalls surrounding the holes to form a printed circuit completelyencapsulated with the cylinder of acrylic resin.

The particular amounts of catalytic agent shown as specific examplesherein are operable, although the preferred amounts for obtaining arapid electroless deposition While using a reasonable amount ofcatalytic agent is between 10 and 20% by weight. The initial copperdeposition obtaincd with these amounts occurs within about 13 2 tominutes after immersion in the electroless plating bath.

The following figures are included to illustrate the major embodimentsof the catalytic compositions disclosed herein.

FIGURE 1 shows an insulating base 1 which has ranthere is randomlydistributed particles of cuprous oxide 2;

FIGURE 2 shows an insulating support 3 to which there has been laminatedan insulating base 1 in which there is randomly distributed particles ofcuprous oxide 2;

FIGURE 3 shows an insulating support 3 having applied on its surfaceparticles of cuprous oxide 1 in the form of filler in an adhesive ink 4;

FIGURES 4, 4a and 4b show an embodiment of a printed circuit in whichthe printed circuit pattern 6 is formed in holes bored into a solid massof an insulating material 8, as described in Example 24; and

FIGURE 4 is an isometric view of the circuit and FIG- URE 4a is a crosssectional view showing how the interconnecting circuit pattern 6comprising the electroless copper deposit 10 runs through the insulatingmaterial 8. FIGURE 4b is an enlarged cross sectional view of theconducting pattern of FIGURE 4a and depicts how the electrolessdeposited copper 10 is adhered to the catalytic composition 12 which inturn is bonded to the lateral wall of insulating material 8 defining theaperture 6.

The FIGURES 1 to 3 show intermediate products resulting from thecarrying out of the methods described in the corresponding examples inthe specification in that FIGURE 1 corresponds to Example 15, FIGURE 2corresponds to Example 16 and FIGURE 3 corresponds to Example 19.

FIGURES 4, 4a and 4b are schematic illustrations 0 the printed circuitproduced according to the teachings of Example 23.

As is clear from the foregoing examples, the base materials on which themetal is deposited are capable of wide variation in composition andconfiguration. Among base materials to which the catalytic compositionmay be adhered may be mentioned impregnated laminates of paper or cloth,or even Fiberglas. The resin impregnant for such laminates includephenolics, epoxys, polyesters, and the like. When impregnated laminatesare used, it is desirable to pre-coat the laminates with a smoothplastic film prior to adhering the. catalytic composition.

As is also clear from the foregoing examples, the base materials mayinclude molded plastic, such as molded epoxy resin, polyester resin,epoxy resin, and the like.

The base materials may even have incorporated therein the active agentfor reception of the electroless copper deposit, as is clear fromExample 15. In this embodiment, it is not necessary to separately adherethe catalytic composition to the base material, since the base materialitself forms the blank from which printed circuits may be made directly.

Still other possible base materials include lightweight syntheticmaterials well known to the building trade, such as wallboard, Masonite,Transite, and the like. Also may be mentioned anodized aluminum whichhas been sealed in a manner well known in the art to render the anodizedcoating insulating.

Also suitable for use' as the base material are plastic coated articleis heated to fuse the coating. The particles or steel coated with aresin. Such plastic coated metals are well known in the art, and arecommercially available. They may be preparedeither by dip coating, spraycoating, or flame coating metal substrates with a resin. Preferably,however, since smooth surfaces are desired, such metal resin coatedlaminates are prepared by fluidized bed techniques which are now wellknown in the art and described, for example, in US. Patent 3,028,251.

Suitable compositions for use in fluidized bed coating of a metalsubstrate with an insulating coating of a plastic material comprise amixture of fusible epoxy resin and a fusible phenolic type resin. Thecompositions are in the form of free-flowing powders, which are fusibleat an elevated temperature below the temperature at which the resin willbe decomposed during the formation of the coating by fusion.Compositions in which the epoxy resin varies from about 10 to aboutbased upon the total weight of the two resins, are preferred. Thecoating composition may contain other types of resins in addition toepoxy resin and phenolic resin, such as, for example, a polyester resin,a polyamide resin, a melamine formaldehyde resin or a natural resin,such as copal or rosin.

In the fluidized bed coating technique, finely divided solid particlesof the resin composition are fluidized in a stream of gas, such as air,and a pre-heated article to be coated immersed in the fluidized bed forsuitable periods of time. [Following removal from the bed, the coatedarticle is heated to fuse the coating. The particles of resin in thefluidized bed will ordinarily range in size from about 5 to 600 mesh,United States Standard Sieve Series.

The following examples illustrate methods of forming printed circuitsusing plastic coated metal base materials.

EXAMPLE 24 Fifty parts, by weight, of an epoxy resin formed by thereaction of bisphenol A with epichlorohydrin and characterized by anepoxide equivalent (grams of resin containing one gram equivalent ofepoxide) within the range of 1550 to 2000, an equivalent weight of 190,a melting point of 127 C. to 133 C. and a particle size less than 40mesh, fifty parts, by weight, of a phenolic resin produced by thereaction of phenol with formaldehyde and characterized by a softeningpoint of 180 F. to 220 F., a specific gravity of 1.2 and a particle sizeless than 40 mesh and two parts, by weight, of powdered silica having aparticle size ranging from 1 micron to 7 microns were dry blendedtogether.

A pierced and blanked aluminum plate having a thickness of inch, a widthof about 3 inches and a length of about 6 inches was heated to atemperature of 400 F. and while at that temperature immersed in afluidized bed of the dry resin blend for a period of time ranging from Asecond to 2 seconds. Upon removal from the fluidized bed, the coatedpanel was maintained at a temperature of about 400 F. for a period ofabout 15 minutes to cure the coating which had been deposited thereon.Upon curing, the coating on the plate was. found to vary from about 2 to10 mils in thickness, depending upon the time of contact in thefluidized bed. The coating was semi-gloss transparent and showed thenatural color of the aluminum.

The coating extended through the plurality of holes in the panel. Theseholes had an original diameter of about 50 mils.

The resulting plastic coated aluminum was screen printed with thecatalytic ink described in Example 2 to form a conductor pattern. Thecatalytic ink circuit thus outlined was cured to [firmly bond it to thebase. The cuprous 0Xid particles in the catalytic ink were reduced tometallic copper by immersion in sulfuric acid following the procedure ofExample 15. The panel was then immersed in the bath of Example 8 for aperiod of about 36 hours, thereby building up a printed circuit in thesame manner as in the previous examples.

Following electroless copper deposition, the panel was post cured byheating for about 2 hours at C.

-In this embodiment, plated through holes may be readily formed bycoating the lateral walls surrounding the holes with the catalytic inkprior to acid treatment and immersion in the electroless copper bath.

1 5 EXAMPLE 25 Example 24 is repeated with the exception that by weightof cuprous oxide having a particle size of less than 200 mesh, US.Standard Sieve Series, based on the weight of the resin, wasincorporated into the resinous composition prior to blending.

A pierced and blanked aluminum plate was anodized and coated with theresulting composition using the technique described in Example 24.

The plastic coating contained particles of cuprous oxide finelydispersed throughout. To form the printed circuit, the surface of thepanel was coated with a masking composition which left exposed aconductor pattern and also the lateral walls surrounding the holes. Thepanel was then immersed in sulfuric acid having the strength of about25% for about 5 to 15 minutes to reduce at least a portion of thecuprous oxide to copper in the exposed areas of the conductor patternand in the holes. The panel was then immersed in the electroless copperplating bath of Example 9 for about 75 hours, at the end of which time afirmly adherent, ductile, and bright electroless copper deposit hadbuilt up on the conductor pattern and on the lateral walls surroundingthe holes.

In this example, the holes in the aluminum panel were coated by thefluidized bed technique, so that the holes actually had cuprous oxideparticles adhered to the lateral sides of the holes. The wallsurrounding the holes, in other words, following activation of thecuprous oxide with the acid, contained sites catalytic to electrolesscopper deposition. Accordingly, when the panel was submerged in theelectroless copper bath, the walls surrounding the holes also received auniform adherent deposit of electroless copper.

As will be clear, the technique described in this example is suitable tomake printed circuits on both sides of an insulating panel with platedthrough holes directly. Heretofore, great difficulty has beenexperienced in the trade in making plated through holes usingelectroless deposition techniques. The procedure outlined in Example 25as well as certain of the other examples contained herein, represents asignificant advancement in the art of making plated through holes.

If desired, special properties may be imparted to the copper conductingpatterns produced as disclosed herein, as for example by depositingnickel, gold, silver, rhodium, and similar metals on the copperconducting pattern in whole or in part.

Typical nickel baths which may be used to deposit the additional metalsare described in Brenner, Metal Finishing, 1954, pages 68 to 76, andcomprise acidic aqueous solutions of a nickel salt, such as nickelchloride; an active chemical reducing agent for the nickel salt, such asa hypophosphite; and a complexing agent, such as carboxylic acid andsalts thereof. Suitable electroless gold plating baths which may be usedto deposit additional metal are disclosed in US. Patent 2,976,181, andcontain a slightly water soluble gold salt, such as gold cyanide, areducing agent for the gold salt, such as the hypophosphite ion, and achelating or complexing agent, such as sodium and potassium cyanide. Thehypophosphite ion may be introduced in the form of hypophosphorous acidand salts thereof, such as sodium, calcium and ammonium salts.

It should be clear from the foregoing examples that when the embodimentusing the adhesive resin ink is employed, printed circuits may be madeby employing either the direct or reverse printing technique. Also,following formation of the conductor pattern, the copper circuit can bedip soldered in whole or in part. If only portions of the circuit are tobe dip soldered, a permanent or non-permanent solder mask may be used tocoat the conductor pattern prior to dip soldering. Also, if desired, theconducting copper pattern, either in whole if? or in part, may receivean additional coating of metal, such as gold, silver, rhodium and thelike, to impart special properties to the circuit as a whole ordesignated portions thereof.

It should be also be clear form the foregoing that completed circuitswith plated through holes can be readily and facilely made according tothe techniques disclosed herein, including modifications of suchtechniques which will be obvious to those skilled in the art.

The invention in its broader aspects is not limited to the specificsteps, methods, compositions and improvements shown and describedherein, but departures may be made within the scope of the accompanyingclaims without departing from the principles of the invention andwithout sacrificing its chief advantages.

What is claimed:

1. A process for metallizing insulating base materials which comprisesadhesively binding to surfaces of the base material an agent catalyticto the reception of electroless copper, and then immersing the basematerial in an alkaline electroless copper depositing bath comprisingwater, a water soluble cupric salt, a complexing agent for cupric ion, areducing agent for cupric ion, and a complexing agent for cuprous ion,to thereby build up an adherent, ductile layer of electrolesslydeposited copper at sites where the catalytic agent is exposed to thebath.

2. The process of claim 1 wherein the catalytic agent is finely dividedcuprous oxide, and wherein the cuprous oxide is reduced at least in partto copper prior to immersion in the alkaline copper electrolessdeposition bath.

3. The process of claim 1 wherein the catalytic agent is adhesivelybound to the surfaces of the base material by incorporating thecatalytic agent into an adhesive resin ink, applying the ink to the basematerial, and then curing the ink.

4. The process of claim 1 wherein the catalytic agent is adhesivelybound to the surface of the base material by forming a strip of a resincontaining the catalytic agent and adhesively adhering the strip to thebase material.

5. The process of claim 1 wherein the base material is a molded resinhaving the catalytic agent dispersed therein.

6. The process of claim 1 wherein the complexing agent for cuprous ionis a water soluble cyanide salt.

7. The process of claim 1 wherein the aqueous alkaline electrolesscopper depositing bath comprises: about 0.02 to 0.15 mol. per liter of awater soluble copper salt, about 0.06 to 3.4 mols. per liter offormaldehyde; about 0.5 to 2.5 times the mols of copper of a complexingagent for cupric ion; as the cuprous complexing agent, about 0.00002 to0.06 mol. per liter of a water soluble cyanide compound; and enough ofan alkali metal hydroxide to give a pH of about 10.5 to 14.

8. The process of claim 1 wherein, as the alkaline electroless copperdepositing bath, there is used an alkaline solution which compriseswater, a water soluble copper salt, a complexing agent for cupric ion, areducing agent for cupric ion, and a small effective amount of a watersoluble cyanide compound.

9. A method of forming printed circuits which comprises preparing aplastic laminate by molding an adhesive resinous composition havingdispersed therein finely divided solid particles of an agent catalyticto the reception of electroless copper and selected from the groupconsisting 'of titanium, aluminum, copper, iron, cobalt, zinc, copperoxide and titanous oxide, including mixtures of the foregoing; masking aportion of the surface of the resulting plastic article to leave exposeda circuit design; and immersing the article in an alkaline electrolessplating bath comprising water, a water soluble cupric salt, an alkalimetal hydroxide, a complexing agent for cupric ion, formaldehyde, and acomplexing agent for cuprous ion, to thereby build up an adherentductile layer of electrolessly deposited copper at sites on the surfaceof the laminate where the catalytic agent is exposed to the bath.

10. A method of forming printed circuits which comprises preparing amolded, three-dimensional article of a plastic insulating materialhaving uniformly dispersed throughout finely divided solid particles ofan agent catalytic to the reception of electroless copper; establishinginterconnecting channels inside of the article to define a circuitpattern and to expose myriad sites of the catalytic agent on the wallsdefining the channels; and immersing the article in an electrolesscopper bath comprising water, a water soluble copper salt, an alkalimetal hydroxide, a complexing agent for cupric ion, formaldehyde, and acomplexing agent for cuprous ion, to thereby build up an adherent layerof electrolessly deposited copper at the sites on the walls defining thechannels where the catalytic agent is exposed to the bath.

11. A method of forming printed circuits which comprises coating atleast selected areas of an insulating base material with an inkcomprising an adhesive resin having dispersed therein an agent catalyticto the reception of electroless copper; and immersing the resultinginsulating base material in an alkaline electroless copper bathcomprising water, awater soluble cupric salt, a complexing agent forcupric ion, a reducing agent for cupric ion, and a complexing agent forcuprous ion, to thereby build up an adherent, ductible layer ofelectrolessly deposited copper at the sites where the catalytic agent isexposed to the bath.

12. The method of claim 11 wherein, as the alkaline electroless copperdepositing bath, there is used an alkaline solution which compriseswater, a water soluble copper salt, a complexing agent for cupric ion, areducing agent for cupric ion, and a small effective amount of a watersoluble cyanide compound.

13. The method of claim 11 wherein the ink comprises, in combination, athermosetting resin which is a member selected from the group consistingof phenolic resins, polyester resins, epoxy resins, and mixtures of theforegoing; and an adhesive resin which is a'member selected from thegroup consisting of epoxy resin, polyvinyl acetal resin,butadiene-acrylonitrile resin, chlorinated rubber, and mixtures of theforegoing.

14. A method of forming printed circuits which comprises providinginterconnecting apertures in a solid insulating material ofpredetermined configuration; coating the lateral Walls of the apertureswith an adhesive resin ink having dispersed therein finely divided solidparticles of an agent which is catalytic to the reception of anelectroless copper deposit; curing the resin to adhesively bond thecatalytic agent to the walls; and immersing the article in an aqueousalkaline solution comprising water, a water soluble cupric salt, :analkali metal hydroxide, a complexing agent for cupric ion, formaldehyde,and a complexing agent for cuprous ion, to thereby build up an adherentductile layer of electrolessly deposited copper at the sites where thecatalytic agent is exposed to the bath.

15. A process for making printed circuits which comprises providingholes in a metal plate at points defining cross-overs between the topand bottom surfaces of the plate; coating the surfaces of the plateincluding the Walls surrounding the apertures with a film of aninsulating resinous material by heating the plate and immersing it in afluidized bed of finely divided particles of the resinous material;coating at least selected areas of the resulting panel with an inkcomprising an adhesive resin base having dispersed therein at numerousindividual sites finely divided particles of an agent catalytic to thereception of electroless copper; curing the ink to adhesively bond thecatalytic agent to the base; and immersing the resulting panel in analkaline electroless copper bath comprising water, a water solublecupric salt, an alkali metal hydroxide, a complexing agent for cupricion, formaldehyde, and a complexing agent for cuprous ion, to therebybuild up an adherent, ductile layer of electrolessly deposited copper atthe sites where the catalytic agent is exposed to the bath.

-16.- The process of claim 15 wherein the lateral walls of the panelsurrounding the apertures are coated with said ink, and wherein aductile copper deposit is built up on said walls'when the panel isimmersed in the alkaline elec troless copper depositing bath.

17. A process for making printed circuits which comprises providingapertures in a metal plate at points defining cross-overs between thetop and bottom surfaces of the plate; anodizing the plate to render itnon-conducting; coating the surfaces of the anodized metal plate and thewalls surrounding the apertures with a composition comprising anadhesive resin having dispersed throughout finely divided solidparticles of an agent catalytic to the reception of electroless copperby heating the plate and immersing it in a fluidized bed of finelydivided solid particles of the adhesive resin composition; maskingselected portions of the surfaces of the resulting resin coated panel toleave exposed a conductor pattern; and immersing the resulting panel inan aqueous alkaline electroless depositing bath comprising water, awater soluble cupric salt, an alkali metal hydroxide, a complexing agentfor cupric ion, formaldehyde, and a complexing agent for cuprous ion, tothereby build up an adherent layer of electrolessly deposited copper atthe sites where the catalytic agent is exposed to the bath.

18. A process for simultaneously depositing and tenaciously adhering alayer of ductile electroless copper having a uniform thickness on aninsulating substratum which comprises adhesively binding to surfaces ofthe insulating substratum an agent which is catalytic to the receptionof electroless copper and then contacting the substratum with analkaline aqueous electroless copper depositing solution comprising awater soluble copper salt, a complexing agent for cupric ion, a reducingagent for cupric ion, and a complexing agent for cuprous ion.

19. The process of claim 18 wherein the cuprous ion complexing agent isa Water soluble cyanide compound.

20. The method of claim 18 wherein the reducing agent for cupric ion isformaldehyde.

21. The method of claim 18 wherein, as the alkaline electroless copperdepositing bath, there is used an alkaline solution which compriseswater, a water soluble copper salt, a complexing agent for cupric ion, areducing agent for cupric ion, and a small effective amount of a watersoluble cyanide compound.

22. A method of forming metallized assemblies comprising an insulatingbase having a relatively thin film of metal adhered to a portion thereofwhich comprises es tablishing a three-dimensional insulating basecomprising as adhesive resinous composition having dispersed therein anagent catalytic to the reception of electroless copper, and exposing atleast a portion of said insulating base to a stable alkaline electrolesscopper plating solution capable of forming a ductile electroless copperdeposit and comprising a water soluble cupric salt, water, a complexingagent for cupric ion, a reducing agent for cupric ion, and a complexingagent for cuprous ion, to thereby build up an adherent layer ofelectrolessly deposited copper at sites on the surfaces of theinsulating base where the catalytic agent is exposed to the bath.

23. The methodof claim 22, wherein in the alkaline electroless copperplating solution, the reducing agent for cupric ion is formaldehyde, andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

24. A method of metallizing interior portions of a three-dimensionalinsulating base material, which comprises, establishing athree-dimensional insulating base of an adhesive resinous compositioncontaining an agent catalytic to the reception of electroless copper andcontaining at least one open, interior channel, said adhesive resinouscomposition forming the surrounding wall of said channel; and immersingthe resulting insulating base in an alkaline electroless copper platingsolution capable of forming a ductile electroless copper deposit andcomprising water, a water soluble copper salt, a complexing agent forcupric ion, a reducing agent for cupric ion, and a complexing agent forcuprous ion, to thereby build up an adherent layer of electrolesslydeposited copper on the Wall of the adhesive resinous compositionsurrounding the channel wherever the catalytic agent dispersed thereinis exposed to the bath.

25. The method of claim 24, wherein in the alkaline electroless copperplating solution, the reducing agent for cupric ion is formaldehyde andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

26. A method of making printed circuits which comprises establishing amolded insulating base comprising an adhesive resinous compositioncontaining an agent catalytic to the reception of electroless copper;masking a portion of the surface of the resulting insulating base toleave exposed a circuit design; and immersing the resulting base in analkaline electroless copper plating bath capable of forming a ductileelectroless copper deposit comprising water, a water soluble cupricsalt, a complexing agent for cupric ion, a reducing agent for cupricion, and a complexing agent for cuprous ion, to thereby build up anadherent layer of electrolessly deposited copper on the exposed circuitdesign.

27. The method of claim 26, wherein in the alkaline electroless copperplating solution, the reducing agent for cupric ion is formaldehyde, andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

28. A method of forming printed circuits which comprises establishing athree-dimensional insulating base comprising a resinous compositioncontaining an agent catalytic to the reception of electroless copper,said base having at least one interior channel defining at least aportion of a circuit pattern; said channel being surrounded by a wall ofsaid resinous composition; and immersing the base in a stable alkalineelectroless copper bath comprising water, a water soluble copper salt, acomplexing agent for cupric ion, and a reducing agent for cupric ion, tothereby build up an adherent layer of electrolessly deposited copper atsites on the wall of the channel Where the catalytic agent is exposed tothe bath.

29. The method of claim 28 wherein in the electroless copper platingsolution, the reducing agent for cupric ion is formaldehyde, and whereinthe copper plating solution comprises a small effective amount of awater soluble cyanide compound.

30. 'A method for making printed circuits which comprises providingholes in a resinous insulating base material said holes definingcross-overs between the top and bottom surfaces of said base, coating atleast a selected area of the resulting basewith an ink comprising anadhesive resinous composition containing an agent catalytic to thereception of electroless copper, curing the ink to adhesively bond thecatalytic agent to the base and immersing the resulting panel in analkaline electroless copper plating solution capable of forming aductile electroless copper deposit and comprising water, a water solublecopper salt, a complexing agent for cupric ion, a reducing agent forcupric ion and a complexing agent for cuprous ion.

31. The method of claim 39, wherein in the alkaline electroless copperplating solution the reducing agent for cupric ion is formaldehyde andwherein said solution contains a small effective amount of a Watersoluble cyanide compound.

32. A method of making printed circuits which comprises providinginterconnecting apertures in a solid insulating resinous base material,coating the lateral walls of the apertures with an adhesive resinouscomposition containing an agent catalytic to the reception ofelectroless copper, curing the resin to adhesively bond the resinouscatalytic agent to the resinous base, and immersing the article in anaqueous alkaline electroless copper plating solution capable of forminga ductile electroless copper deposit and comprising water, a watersoluble copper salt, a complexing agent for cupric ion, a reducing agentfor cupric ion, and a complexing agent for the cuprous ion.

33. The method of claim 32, wherein in the alkaline electroless copperplating solution the reducing agent for cupric ion is formaldehyde andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

34. A method of making printed circuits which comprises providingapertures in a metal plate at points defining cross-overs between thetop and bottom surfaces of the plate, coating the surfaces of the plateincluding the walls surrounding the apertures with a film of aninsulating resinous material, coating at least selected areas of theresulting panel with an adhesive resinous composition containing anagent catalytic to the reception of electroless copper, curing theresulting catalytic agent to adhesively, bond the catalytic agent to thebase, and immersing the resulting panel in an alkaline electrolesscopper plating solution capable of forming a ductile electroless copperdeposit and comprising water, a water soluble copper salt, a complexingagent for cupric ion, a reducing agent for cupric ion, and a complexingagent for the cuprous ion.

35. The method of claim 34, wherein in the alkaline electroless copperplating solution the reducing agent for cupric ion is formaldehyde andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

36. A method for making printed circuits which comprises providingapertures in a metal plate at points defining cross-overs between thetop and bottom surfaces of the plate, coating the surfaces of the platewith a non-conducting material including the walls surrounding theapertures, said non-conducting material comprising an adhesive resinouscomposition containing an agent catalytic to the reception ofelectroless copper, masking selected portions of the surfaces of theresinous coated panel to leave exposed a conductor pattern, immersingthe resulting panel in an alkaline electroless copper plating solutioncapable of forming a ductile electroless copper deposit and comprisingwater, a water soluble copper salt, a complexing agent for cupric ion, areducing agent for cupric ion and a complexing agent for cuprous ion.

37. The method of claim 36, wherein in the alkaline electroless copperplating solution the reducing agent for cupric ion is formaldehyde andwherein said solution contains a small effective amount of a watersoluble cyanide compound.

38. The process for making printed circuits which comprises providingapertures in a metal plate at points defining cross-overs between thetop and bottom surfaces of the plate; coating the surfaces of the plate,including the walls surrounding the apertures with a film of aninsulating resinous material comprising an adhesive resin base havingdispersed therein at numerous individual sites finely divided particlesof an agent catalytic to the reception of electroless copper by heatingthe plate and immersing it in a fluidized bed of finely dividedparticles of said adhesive resinous material curing said adhesiveresinous material to adhesively bond said resinous material andcatalytic agent to said plate and immersing the resulting panel in anelectroless copper bath comprising water, a water soluble cupric salt,an alkali metal hydroxide, a complexing agent for cupric ion, a reducingagent for the cupric ion and a complexing agent for the cuprous ion tothereby build up an adherent ductile layer of electrolessly depositedcopper on the sites where the catalytic agent is exposed to the bath.

39. The process of claim 38, wherein selected portions of the surfacesof the resulting resin coated panel are masked to leave exposed aconductor pattern and subsequently immersing the masked panel in saidelectroless depositing bath.

40. A process for making printed circuits which comprise providing holesin an insulating base at points defining cross-overs between the top andbottom surfaces of the base, said insulating base containing dispersetherein an agent which is catalytic to the reception of electrolesscopper deposit; coating said base with a resist material leaving exposedthose areas defining the desired circuit pattern and said cross-overs;and immersing said base in an electroless copper deposit bath whichcomprises a water soluble salt, a complexing agent for cupric ion, acomplexing agent for cuprous ion and a reducing agent for cupric ion.

41. The process of claim 40, wherein said catalytic agent comprisessolid particles of finely divided catalytic material.

42. The process of claim 41, wherein said catalytic agent comprisesfinely divided solid particles of copper oxide.

43. A process for making printed circuits which comprises putting holesin an insulating base at points defining cross-overs between the top andbottom surfaces of the base, said base containing dispersed therein anagent which is catalytic to the reception of electroless copper deposit;coating at least a selected area of one of the top and bottom surfacesof said base with an adhesive resin ink having dispersed therein finelydivided solid particles of an agent which is catalytic to the receptionof an electroless copper deposit; and immersing the resulting panel inan alkaline electroless copper plating solution capable of forming aductile electroless copper deposit and comprising water, a water solublecopper salt, a complexing agent for cupric ion, a reducing agent forcupric ion and a complexing agent for cuprous ion.

44. The process of claim 43, wherein the top and bottom surfaces of saidpanel are coated with said adhesive resin ink, said ink is cured toadhesively bond the catalytic agent to said base, and coating selectedareas of said top and bottom surfaces of said panel with a resistmaterial leaving exposed those areas defining the desired circuitpattern and said cross-overs.

45. The process of claim 43, wherein the top and bottom surfaces of saidpanel are coated with a resist material and at least a selected area ofsaid resist material is coated with said adhesive resin ink in a patterndefining the desired circuit configuration and curing the ink toadhesively bond the catalytic agent to the base.

References Cited by the Examiner UNITED STATES PATENTS 2,731,672 1/ 1956Davis et al. 264132 2,874,416 2/ 1959 Burnett 264132 2,882,187 4/1959Kwate 117-227 2,939,807 6/ 1960 Needham 117-217 3,019,283 1/1962 Little174-685 3,031,344 4/ 1962 Sher et al. 117-212 3,032,443 5/1962 Short117-212 3,053,929 9/1962 Friedman 174-685 3,060,062 10/ 1962 Katz et al117-112 3,075,856 1/1963 Lukes 117-212 3,079,672 3/1963 Bain et al.29-1555 3,081,525 3/ 1963 Delbove 29-1555 3,095,309 6/1963 Zeblisky etal. 106-1 3,119,709 1/ 1964 Atkinson.

3,134,690 5/1964 Eriksson 117-212 3,146,125 8/1964 Schneble et a1117-212 3,154,478 10/1964 Lee 106-1 3,171,756 3/ 1965 Marshall 117-227RICHARD D. NEVIUS, Primary Examiner.

WILLIAM D. MARTIN, W. L. JARVIS,

Assistant Examiners.

17. A PROCESS FOR MAKING PRINTED CIRCUITS WHICH COMPRISES PROVIDING APERTURES IN A METAL PLATE AT POINTS DEFINING CROSS-OVERS BETWEEN THE TOP AND BOTTOM SURFACES OF THE PLATE; ANODIZING THE PLATE OF RENDER IT NON-CONDUCTING; COATING THE SURFACES OF THE ANODIZED METAL PLATE AND THE WALLS SURROUNDING THE APERTURES WITH A COMPOSITION COMPRISING AN ADHESIVE RESIN HAVING DISPERSED THROUGHOUT FINELY DIVIDED SOLID PARCLES OF AN AGENT CATALYTIC TO THE RECEPTION TO ELECTROLESS COPPER BY HEATIING THE PLATE AND IMMERSING IT IN A FLUIDIZED BED OF FINELY DIVIDED SOLID PARTICLES OF THE ADHESIVE RESIN COMPOSITION; MASKING SELECTED PORTIONS OF THE SURFACES OF THE RESULTING RESIN COATED PANEL TO LEAVE EXPOSED A CONDUCTOR PATTERN; AND IMMERSING THE RESULTING PANEL IN AN AQUEOUS ALKALINE ELECTROLESS DEPOSITING BATH COMPRISING WATER, WATER SOLUBLE CUPRIC SALT, AN ALKALI METAL HYDROXIDE, A COMPLEXING AGENT FOR CUPRIC ION, FORMALDEHYDE, AND A COMPLEXING AGENT FOR CUPROUS ION, TO THEREBY BUILD UP AN ADHERENT LAYER OF ELLECTROLESSLY DEPOSITED COPPER AT THE SITES WHERE THE CATALYTIC AGENT IS EXPOSED TO THE BATH. 